Someone please educate me on a torque converter?
#2
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In the most over simplistic terms, if you press the gas and the tach moves in direct proportion to the speed, it is locked up. If it rises to say, 2k rpm, and stays there as the car continues to gain speed it is not locked up (common scenario: moving from a stop). Different cars lock up at different times- the most efficient transmissions stay locked as much as possible.
#3
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In the most over simplistic terms, if you press the gas and the tach moves in direct proportion to the speed, it is locked up. If it rises to say, 2k rpm, and stays there as the car continues to gain speed it is not locked up (common scenario: moving from a stop). Different cars lock up at different times- the most efficient transmissions stay locked as much as possible.
You're good at Layman's terms!!!!
#4
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In the most over simplistic terms, if you press the gas and the tach moves in direct proportion to the speed, it is locked up. If it rises to say, 2k rpm, and stays there as the car continues to gain speed it is not locked up (common scenario: moving from a stop). Different cars lock up at different times- the most efficient transmissions stay locked as much as possible.
#5
Lexus Test Driver
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with the aisin transmissions it generally doesn't lock until you're cruising in the highest gear, but yes easiest way to tell is that the rpms and speed will be locked into a certain ratio, just like in a manual trans
the lockup is usually done through some kind of flex plate clutch
the lockup is usually done through some kind of flex plate clutch
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#8
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well yes but in the case of his cars we're dealing with 2 more old school aisin transmissions so that's what i meant... i should've been more clear
#9
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Ok let's take this further. What the hell is a stall speed? I remember sport equipped E38 7 series had a "high stall speed torque converter". What does that mean?
#10
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Actually, the term you are looking for is called "Slippage". It means, as TangoRed alluded to in his first post, that the fluid-coupling in the transmission allows some "Slip" or excess engine-RPM, over the transmission's output-shaft. The engine will turn at a slightly higher RPM while cruising (and substantially higher RPM while accelerating) than if the system were locked, or with a straight mechanical hook-up like in a manual transmission. The torque converter locks up and prevents that slippage except at very low speeds or gear-ratios.....otherwise the engine would lug severely or stall. Some transmissions, in the quest for smoothness, used to allow an extreme amount of slippage, particularly on start-up from rest......Buick's old Dynaflow from the 40s and 50s, with no mechanical connections at all in the transmission (completely fluid-drive, with pitch-stators), was notorious for that, and for wasting fuel.
Chrysler was the first American manufacturer to introduce lock-up converters in modern times, in 1978, on its RWD Three-Speed Torqueflite-automatic-equipped vehicles. It did help with gas-mileage at a time when CAFE regulations were getting stricter, but, until the system was refined, was also the source of customer complaints from engine-lugging, and stalling if the system malfunctioned.
#11
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Stall speed is the engine-RPM that is needed before the power (torque) of the engine overcomes the drag in the torque-converter, gets the transmission's output-shaft spinning, and actually starts the vehicle moving. The higher the stall speed, the less efficient the transmission, and the more you will have to push the gas pedal to overcome the drag and get the vehicle moving. This is why, for automatic transmissions used in drag-racing, a low stall-speed is desired.....for quicker response when the light turns green and you want to start moving.
#12
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Stall speed is the engine-RPM that is needed before the power (torque) of the engine overcomes the drag in the torque-converter, gets the transmission's output-shaft spinning, and actually starts the vehicle moving. The higher the stall speed, the less efficient the transmission, and the more you will have to push the gas pedal to overcome the drag and get the vehicle moving. This is why, for automatic transmissions used in drag-racing, a low stall-speed is desired.....for quicker response when the light turns green and you want to start moving.
#13
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Stall speed is the engine-RPM that is needed before the power (torque) of the engine overcomes the drag in the torque-converter, gets the transmission's output-shaft spinning, and actually starts the vehicle moving. The higher the stall speed, the less efficient the transmission, and the more you will have to push the gas pedal to overcome the drag and get the vehicle moving. This is why, for automatic transmissions used in drag-racing, a low stall-speed is desired.....for quicker response when the light turns green and you want to start moving.
In the case of the 740i, it allows the engine to be higher in its powerband and therefore create more power before the torque converter locks. Makes for a better launch.
Ah ok that makes sense.
#14
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Stall speed is the engine-RPM that is needed before the power (torque) of the engine overcomes the drag in the torque-converter, gets the transmission's output-shaft spinning, and actually starts the vehicle moving. The higher the stall speed, the less efficient the transmission, and the more you will have to push the gas pedal to overcome the drag and get the vehicle moving. This is why, for automatic transmissions used in drag-racing, a low stall-speed is desired.....for quicker response when the light turns green and you want to start moving.
From folks who actually build these things for a living:
Some people believe that "stall" means the car won't start moving until the engine reaches that particular RPM, and that isn't even close to being true. We build race cars with 6,000 RPM stall converters and when you put the car in gear and let it idle, it WILL roll along at 5 - 10 MPH, just like any other car will when put in gear and with the brake off. In fact, we usually cruise through the pits with the car simply in gear and idling, so if a 6,000 RPM converter means that the car won't start moving UNTIL that RPM, then we'd have to have the engine wound-out to 6,000 RPM to putt along through the pits at 10-15 MPH, and that simply isn't the case. Stall means when the car is on the starting line, (with say a 4,500 RPM stall converter), and the trans brake is on, (which locks the transmission in first and reverse at the same time), and you hit full throttle, the engine will wind-up to 4,500 RPM with the car just sitting there, so when you slip your finger off the trans brake button and the tranny engages out of reverse, the car instantly launches at 4,500 RPM, and a race motor at 4,500 RPM is pretty close to its peak torque curve when leaving the line, hence the big wheelies you see on some drag cars or the incredibly low 60 Ft. times when traction is good. Race engines make no power at low RPM's, and are usually shy on torque, so the nastier the engine, the higher the stall speed needs to be (in general anyway).
source
#15
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That's not totally correct info. Drag racers prefer high stall speed torque converters. It puts the engine in its powerband (ideally at the rpm where the engine creating maximum torque) while doing a brake-torque launch so the engine is creating maximum power right from the start.
Originally Posted by geko29
Dedicated drag cars use high-stall torque converters ("mild" 9-10 second cars tend to use converters that stall between 3,500 and 4,500 rpm, the crazy-fast ones may use 6,000 rpm converters), because they want to be able to launch with the engine already in the powerband.